The art of filtration, broadly speaking, is generally represented by various hydro-mechanical or chemically oriented apparatus and procedures whereby impurities are removed from a flow of liquid, usually water. The basic types of filtration arrangements and devices of the prior art, and their accompanying problems and limitations, may be categorized, generally as follows:
1. Non-regeneration modular filters are one time, short use, devices of inexpensive cartridge design that have low flow-high head loss limitations of which the filter material involved is packed cellulose or fibronous textile material that at the optimum best will provide no better than 5-10 micron absolute particle size filtration results. Minor recognizeable suspended solids in the fibrant will quickly clog the filter material within the cartridge and render the filter system involved inoperable. Where moderate and high flow rate is involved, replacement costs and down time are inordinantly burdensome.
2. Regenerative membrane (rotary and stationary types) filters are relatively expensive, and while they may involve filtered water backwash design, they are limited to tertiary or polishing water filtration wherein suspended solids contamination is relatively light and can be removed at the 10-15 part per million level. These filters are generally not efficient in removing solids debris below the 5-10 micron particle size level, and they exhibit low flow filtration characteristics (below 100 gallons per minute) even when effective in the 1-5 micron particle range. Membrane filters foul readily with biological growth inherent to the passing liquid flow, and often become inoperative or highly restrictive to the flow of the filtrant therethrough.
3. Pressurized pre-coated filters are filters of the pressure vessel type that are heavy, bulky, and expensive, and are characterized with costly filtered coatings in the form of diatomaceous earth, fly ash, or the like for filtering and entrapping the suspended solid debris from the passing liquid flow. While precoated filter aids of the type indicated can effectively filter down to the 1 micron particle size level at low filtrant flow rates, at higher, more desirable output flows of 150 gallons per minute (GPM) they tend to become plugged with solids and/or start to dissolve rapidly. As these filter aid precoat materials cannot be regenerated and filter life is short, disposal of contaminated precoat aids presents serious disposal problems that frequently violate the EPA Hazardous Waste definition.
4. High rate sand filtration pressure vessel flters accommodate filtration of relatively large volumes of water (500-1,000 GPM), with reverse filtration water flow along with compressed air providing backwash regeneration of the sand filter material. However, the backwash waste water volume is substantial, as is the cost of the basic system involved. While appropriate selection of sand grain size as filter material will allow volume removal of suspended solid debris down to the 5 micron particle size, this is not adequately close to the micro size level where at least half of the impurities will be found, namely the 1-5 micron particle size, and the dissolved solids particle size range below 1 micron. High rate sand filtration is known to be ineffective for removal of minute particle size debris, and the large volume of backwash water involved in these systems often makes economical disposal impossible.
5. Ion-exchange filters involve filtration systems based on known water chemistry criteria that dissolved contaminating solids are composed of electrically charged molecules and ions. In the filter devices involved, the filter containers are packed with resin material having active site electrical ionic polarity positions therein. A moderate low (200 GPM) ion exchange filter system represents a complex plumbing network involving unwieldy resin filter containers and large installation space requirements. Regeneration of the filter resin becomes complicated and often incomplete due to the plugging of the resin pore spaces by the larger particle size suspended solids of the filtrant. The systems have substantial limitations limiting their practicality for general purpose use because filtration is available for only very select waste waters that must possess very little suspended solids contamination and cannot exceed narrow limits of dissolved chemical contaminants, as well as high cost.
6. Reverse osmosis filters require costly high pressure pumping equipment for moderate outflow apparatus with initial investment, and operating electrical and pressure system maintenance economics that are operationally prohibitive from a practical standpoint. The backwash brine flow required to remove solids from the membrane filter involved periodically causes partial contamination of the filter water flow and reduces the quality of the water filtrate. Reverse osmosis backwash flow volumes often represent 30 to 40 percent of the through-put filtration flow, and therefore the systems provide only a relative low yield of filtered water per unit of capital investment cost, and then only for very select water stream filtration. These systems become inefficient when a multiplicity of contaminating dissolved solids (ions) and suspended particulate contaminants are present that cause membrane fouling.
A principal object of the present invention is to provide a recirculating filtration system for filtering liquids that will effect removal from the filtrant submicroscopic contaminating dissolved solids (in ion form) and suspended particulate solids that may be in the form of foreign matter particulate material that are of either organic or inorganic origin at a predictable particle size approximating 1 micron, while at the same time providing a compact, light weight, regenerative, and economical apparatus or device for that purpose.
Another princial object of the invention is to provide a method and apparatus of electro-chemical filtration of liquids in which basically the same filtration apparatus or device may be employed for both oils and waters, and in which the practice of the invention provides removal of toxic organics, scale and water solids, biological organism contaminants and other foreign matter from the liquid, with efficiencies approaching 100 percent.
Another principal object of the invention is to provide an electro-chemical filtration system that is oriented toward taking advantage of the conductive properties of the liquids to be filtered, such as natural particle debris is water, that effects undesirable ion and colloidal particle removal by way of coagulation, agglomeration, or flocculation of same into larger particle size for entrapment in a two stage polarized filter medium, with efficient regeneration of the filter units involved being provided for by way of backwash procedures that may be built into the system for automatic operation.
Another important object of the invention is to provide an electro-chemical system of filtration, and specifically methods and devices or apparatus arranged in accordance with said system, that is economical of manufacture, compact, light in weight, uncomplicated, and safe in design, that is adaptable for application to a wide variety of liquid filtration needs and requirements, and that is long lived, efficient, and easy to use in operation.
In accordance with the invention, a basic electro-chemical liquid filtration device is provided comprising a canister in cylindrical form that has a bore extending longitudinally thereof and in use is adapted to be vertically position oriented when installed for operating purposes. The canister at its upper end is adapted for connection to the source of the liquid filtrant, and the lower end of the canister is closed to seal same off but provide for periodic removal of foreign materials collecting at the lower end of the canister. The canister adjacent its lower end has a cross tube extending crosswise through same and fixed to same that has a width that is less than the width of the bore on the order of 25 percent, with the cross tube being centered on the longitudinal axis of the canister and having its external surfacing in sealed relation thereabout with the canister at either end of the cross tube. Centered within the cross tube is a tubular mandrel that extends substantially coextensive with the cross tube, with the portions of the cross tube and mandrel that are disposed within the canister each being formed to define multiple liquid passing apertures or orifices thereabout, with the aperture or orifice area total of the cross tube apertures being greater than the corresponding total area of the mandrel tube total orifice or aperture areas by about 25 percent. Interposed between the cross tube and the mandrel is an elongate composite filter sheeting tightly convoluted about the mandrel and in close fitting relation in the space between the mandrel and the cross tube, with the convoluted composite filter sheeting comprising a pair of foraminous electrically conductive corrosion free sheets that each may be in the form of stainless steel wire mesh, separated by a sheet of fibrous material of such fiber size (diameter and density) that the pore spaces or interstices defined thereby have a size in the range of from about 1 to about 5 microns.
A second, coarser filter unit is disposed across the bore of the canister and located between the upper end of same and the cross tube, and is in the form of a pair of foraminous, electrically conductive, non-corrosive sheets, that may be stainless steel or mesh, separated by layers of fibrous material that may comprise one or more discs of fibers of a suitable diameter and density to provide pore spaces therein that have a size in the range of from approximately 15 to approximately 25 microns as average open space.
In each of these filter units of the canister, the filter units are polarized by connecting the respective sets of foraminous sheets anode-cathode fashion to a low voltage low amp source of direct current, such as a 12 volt 50 amp D.C. power supply system.
The general arrangement involved is arranged to interact with the electrical properties of dispersed ion and solid particulate material, whether dissolved or suspended, that might be considered contaminate or otherwise undesirable matter, with filtration removal being accomplished by the passage of the filtrant through the polarized filter units, with the upstream filter unit being of a relatively coarse fiber type to filter out the larger solid particles, and the downstream cross filter unit comprising a relatively fine fiber filter for minute solids and ion removal. Within the two filter units, under the polarization of same that is involved, the solids effect a precoating of the fibers by physical attraction thereto, with the solids becoming electrically charged and attracting other charged solids thereto for coagulation, coalescing and agglomerating of same into larger particle size within the two filter units. The solids tend to form linear molecular chain clusters that become entrapped within the fibrous material involved, with ions being electrically held by the polarization involved within the filter units.
In the general arrangement involved, the filter system canister has its cross tube filter unit arranged for filtrate discharge at either end of same through the mandrel bore, under the control of two three way off-on valves one at either end of the cross tube filter unit, with the entry of the filtrant into the canister being similarly controlled by a similar three way off-on valve. Pursuant to the basic system involved, these three valves are simultaneously controlled for full filtration flow in one position, and for backwash, filter unit regeneration, flow through the canister, in an opposite position, preferably arranged for automatic operation when the psi of the filtrant entering the canister exceeds a predetermined amount, with automatic return to full filtrant flow position after a predetermined time of backwash operation.
The basic recirculating filter system provides for, in conjunction with the discharge of the filtrate from the cross tube filter unit, the injection of ambient air and/or oxidizing gases that for filtration flow purposes may provide for additional oxidation-coagulation of contaminant dissolved solids or other treatment of the effluent, and for backwash purposes provide for gas or air scrubbing of the filtration units as part of the procedure of regenerating same.
Also disclosed is a special gas or air injector device specifically adapted for use in connection with the filtration device or apparatus of this system, that provides dispersed solution gas required for backwashing or for coagulating solids into larger filtrable particle size.
Other objects, uses, and advantages will be obvious or become apparent from a consideration of the following detailed description in conjunction with the application drawings, in which like reference numerals are employed to indicate like parts throughout the several views.